A new strategy that addresses challenges in the field. The lethal and transmissible nature of the paramyxoviruses Hendra virus and Nipah virus (HeV, NiV) makes these pathogens of serious concern. These are also ideal models for developing an innovative new vaccine platform at the interface between bioengineering and virology. A vaccine that targets the paramyxovirus viral fusion protein (F) could provide neutralizing immunity against an important group of human pathogens. The transient activated state of F - exposed only after activation when the receptor binding protein binds receptor, but before fusion - is an optimal target for broadly neutralizing antibodies. We propose to capture and immobilize this activated fusion intermediate, exposing the conserved F domains that are essential for viral entry. We will then use this captured active-state molecule - which is normally highly sheltered from the immune system and could not be properly presented in an immobilized state - to elicit broadly neutralizing antibodies. While this activated conformation is normally present only at the surface of live cells, we propose to use engineered protocells to capture and immobilize this transitional state. Artificial protocells will present the receptor molecules in a biomimetic membrane setting to "trigger" the fusion protein. Three recent advances in our lab make this approach feasible: (1) HeV/NiV are irreversibly inactivated when they interact with receptor moieties that induce the conformational changes in F that lead to fusion-readiness. (2) Lipid-coated silica-based protocells can present receptor molecules on the surface, and irreversibly inactivate paramyxovirus pseudotyped viruses by prematurely triggering the fusion mechanism. (3) Peptides corresponding to the heptad repeats of the fusion protein inhibit fusion/entry by binding only after activation of the conformational change to fusion-readiness, but before progression of fusion. We will use receptor molecules, presented in a biomimetic fashion on the surface of protocells, to activate the conformational change in F, and then use heptad-repeat peptides to arrest F in its activated state and thus immobilize the captured intermediate with the protocell. This complex will then be used to induce neutralizing antibodies. 1. Capture of the activated conformation of Nipah virus fusion (F) machinery: Development of protocells bearing receptor plus peptide, designed to immobilize F in its transition state. Validation of capture mechanism. We will test the hypothesis that protocells bearing receptor plus peptide can effectively trigger and immobilize the intermediate conformational state of F. 2. Use of protocells complexed with F in its activated conformation to elicit immunity. Assessment of immune response. We will test the hypothesis that the exposed transient conformation of F, presented and captured on a biomimetic artificial surface, elicits powerful neutralizing antibodies that inhibit Nipah virus infection. These results will establish a new platform for bioengineering-based vaccination. PUBLIC HEALTH RELEVANCE: Paramyxoviruses cause important human illnesses that contribute significantly to global disease and mortality. The zoonotic paramyxoviruses that are the subject of this application, Hendra virus and Nipah virus, are an urgent concern for public health due to their lethal and transmissible nature. The results of this project will lead to setting up a new bioengineering-based strategy for vaccination that combines new basic findings from virology with new technology to achieve an entirely new approach that of inducing and capturing the relevant activated conformational intermediate of a viral fusion protein. The novel complex will present the key viral antigen in a way normally only seen transiently by the immune system, closely mimicking natural infection. The results will be highly relevant in light of the importance of paramyxoviruses to human health and the potential broad applicability of the bioengineering approach to vaccine development for these and other serious pathogens.